The present invention relates to security alarm systems and, in particular, to a motion detector which finds advantage with normally immobile objects, such as art objects.
Museums, art galleries, collectors and the like are posed with the problem of creating displays which best present a collection, yet protect their collection from theft or tampering. This is oftentimes difficult to achieve without relatively sophisticated or customized security stations.
Hard wired installations can be established for wall, floor or ceiling mounted displays with varying degrees of effort and depending upon the availability of duct work or other conduits for storing and channelling the conductors. Greater flexibility is obtainable with a wireless installation, but heretofore sensors have not been available which accommodate wide varieties of installations. Rather, such installations tend to be customized and use special purpose sensors or sensors in combination with transmitters of relatively large dimension.
Of the latter types of installations, Applicant is aware of assemblies disclosed in U.S. Pat. Nos. 3,247,502 and 4,857,892. Particularly disclosed in these references are devices which protect art objects and sense motion relative to aligned magnets or distributed switch elements mounted within a surrounding framework and backing material. Such devices, however, do not readily find application with sculptural art works or centerpiece type mountings, where the art work is intended to be viewed from all sides.
Applicant is also aware of motion sensing assemblies including piezoelectric elements, such as within various glass breakage sensors. Descriptions of these later devices can be found upon directing attention to U.S. Pat. Nos. 3,863,250; 4,091,660; 4,307,387; 4,758,824 and 4,845,470. Depending upon the circuit construction, various of the foregoing devices detect glass movement relative to a threshold condition and annunciate the movement with an audible alarm. The devices do not provide delayed announcement nor a wireless communication link to a central controller. They are also not particularly sensitive to the rate of change of motion at the piezoelectric element, but rather only to the mere movement.
Another sensor circuit arrangement using piezoelectric elements can be found upon directing attention to U.S. Pat. No. 4,327,359, which discloses a balanced resistive bridge arrangement. U.S. Pat. No. 4,479,110 otherwise discloses a polarity independent detector which is coupled relative to delayed oscillator circuitry. Neither of the later circuits provide a wireless communications link nor are sensitive to the activity level of the piezoelectric elements.
In appreciation of the deficiencies of the art, Applicant has developed the present invention which provides a sensor adaptable to a variety of artwork mountings; which provides multiple annunciation options, either immediately or delayed; which is compatible with multiple communications links; and which is responsive to the activity level or rate of change of the physical sensor element.